New excitation codebook search methods to reduce perceptual degradation of CELP

In this paper, we propose three new excitation codebook search methods for a low-bit-rate CELP coder using an algebraic excitation codebook to reduce code selections that may result in pulse-like degradation. The proposed methods are: (1) adaptive distortion weighting based on the states of the input speech; (2) distortion weighting based on the amplitude distribution of the direction of time; and (3) distortion-ratio limitation to algebraic excitation codebook search. Subjective evaluation results show that the performance of 4 kbit/s CELP is improved by the proposed methods both in clean conditions and with background noise.